Employee Benefit Plans (Net Periodic Benefit Costs) (Details) - USD ($) $ in Millions	3 Months Ended		6 Months Ended
	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Pension Benefits
Net periodic benefit costs [Abstract]
Service costs	$ 73	$ 69	$ 145	$ 138
Interest costs	109	107	220	212
Curtailment costs	0	0	0	0
Expected return on plan assets	(127)	(136)	(254)	(272)
Amortization of net actuarial (gains) losses	50	47	99	95
Amortization of prior service costs (credit)	0	0	0	0
Net periodic benefit costs	105	87	210	173
Other Postretirement Benefits
Net periodic benefit costs [Abstract]
Service costs	2	5	4	9
Interest costs	21	22	42	45
Curtailment costs	(3)	0	27	0
Expected return on plan assets	(19)	(20)	(37)	(40)
Amortization of net actuarial (gains) losses	2	11	4	21
Amortization of prior service costs (credit)	(1)	(1)	(4)	(2)
Net periodic benefit costs	$ 2	$ 17	$ 36	$ 33